Is it still an Outcome of Success if the prize is revealed to have not been worth the cost?
Outcome is nice and clear-cut. If they achieved the Goal, whatever it was, the Outcome is Success. If they did not, the Outcome is Failure.
The only tricky part, sometimes, is figuring out what the Goal is!
Success Outcomes can come with high costs:
Success is success, but maybe the judgment is Bad because of the Cost not being worth it?
Nope. The Judgment has to do with whether there is unresolved angst or not. Judgment has no direct connection to degree of the Story Cost.